Thyroid ablation with 1.1 GBq (30 mCi) iodine-131 in patients with papillary thyroid carcinoma at intermediate risk for recurrence.

BACKGROUND: Little is known about the medium- and long-term outcomes of thyroid ablation with 1.1 GBq (30 mCi) ¹³¹I in patients with papillary thyroid carcinoma who have a tumor >4 cm or accompanied by extrathyroid invasion or clinically detected lymph node metastases (cN1). The objective of this study was to evaluate the efficacy of ablation with 30 mCi ¹³¹I in this subgroup of patients and to report the medium-term outcomes.

METHODS: We studied 152 patients with papillary thyroid carcinoma submitted to total thyroidectomy with apparently complete tumor resection, who had a tumor >4 cm or 2-4 cm accompanied by extrathyroid invasion or lymph node metastases, or ≤2 cm accompanied by both extrathyroid invasion and lymph node metastases. Patients with extensive extrathyroid invasion by the primary tumor were excluded. Lymph node involvement was detected by ultrasonography or palpation (cN1).

RESULTS: Forty-two patients were prepared by administration of recombinant human thyrotropin and 110 by levothyroxine withdrawal. Posttherapy whole-body scanning revealed unequivocal ectopic uptake in three patients. When evaluated 9-12 months after ablation, 123 patients had achieved complete ablation (stimulated thyroglobulin [Tg] <1 ng/mL, negative anti-Tg antibodies, and neck ultrasonography); a new posttherapy whole-body scanning revealed persistent disease in 2 patients whose initial posttherapy whole-body scanning (obtained at the time of ablation) had already shown ectopic uptake; 12 patients presented with a Tg >1 ng/mL and 14 had positive anti-Tg antibodies without apparent metastases; 1 patient had metastases not detected at the time of ablation. Recurrence was observed in an additional 6 patients during follow-up (median 76 months). There was no case of death related to the disease. Therefore, an activity of 30 mCi failed in only 9 (6%) patients with persistent disease or recurrence after ablation. None of the variables analyzed (sex, age, tumor size, multicentricity, extrathyroid invasion, lymph node metastases, preparation [recombinant human thyrotropin or levothyroxine withdrawal]) was a predictor of ablation failure.

CONCLUSIONS: An activity of 30 mCi ¹³¹I is effective in thyroid ablation in patients with stage T3 and/or N1 papillary thyroid carcinoma.